I’ve always wondered why I can fly several time zones west with barely a hint of jet lag but feel like a zombie after journeying just a few hours to the east. So with the winter travel season well underway, I decided to delve into the science.

Anyone who has crossed multiple time zones knows the misery of jet lag. You’re tired when you need to be alert, you can’t sleep when you’re supposed to, and your gastrointestinal system feels out of whack. Researchers have even found signs of memory impairment in female flight attendants with chronic jet lag.

The symptoms of jet lag result from two things: the sleep deprivation and fatigue that come with long stints in a cramped seat, and the misalignment of your body clock with the local time zone, says physician Vivek Jain, medical director of the George Washington University Hospital Center for Sleep Disorders.

Jet lag’s severity depends on several factors, the most obvious being how many time zones you crossed. But which direction you traveled matters, too. Turns out, it’s not my imagination: Going east really does produce worse jet lag.

Traveling west is easier

Your body clock has an innate tendency to run slightly longer than 24 hours, Jain says. Each morning, your body compensates for this slight discrepancy by contracting your internal clock to synchronize with the 24-hour sun cycle. When you travel west, you gain several hours, so your day is extended and your body gets the extra time it naturally wants. But when you travel east, your day is shortened; that makes it harder to adjust, Jain says, because your body has to cut its natural cycle even further.

Studies suggest that you can push your body clock back about two hours per day, meaning that you can adjust from Washington time to Colorado time in a single day, but you can move your body clock forward (as when you travel from California to Washington) only by about an hour to an hour and a half per day, Jain says.

So for Washingtonians flying to see friends or family in California, where it’s three hours earlier, your body clock should be able to adjust in less than two days. But if you’ve got a vacation planned in Paris, where it’s six hours later than here, you’ll likely need three to five days to get in sync.

You can’t entirely prevent jet lag, but you can tame it, experts say. First, time your travel well. Rest up the night before you go, and book a daytime flight if you can. Red-eye flights compound jet lag by heaping sleep deprivation on top of your body clock problems. If you absolutely must take a late-night flight, do what you can to sleep. “Don’t get sucked into watching the movie,” Jain says.

Drink, but not alcohol

Keep hydrated to avoid headaches and lightheadedness, and stay away from alcohol on the plane. Alcohol interferes with sleep, Jain says. Plus, you might end up with a hangover.

If you’re heading east, aim for an evening arrival. “You can do some work on the plane; then when you arrive, you’re tired from the travel and you can have a quick dinner [at the new dinnertime] and be ready to sleep,” Jain says. All of that helps you align with the new time schedule.

Before your trip, ease your transition to the new time zone by moving your bedtime. The American Academy of Sleep Medicine guidelines suggest shifting your sleep schedule an hour earlier each night, starting three days before you leave on an eastbound trip. If that’s impractical, Jain says, try for 15 minutes earlier each night, and get as much early-morning sunlight as you can. Light is the most potent tool for adjusting your body clock: Think of it as a medication that wakes you up, he says.

If you’re traveling east, start seeking bright light first thing in the morning at home. If you’re headed west, though, expose yourself to light in the evening before you leave. That’ll slightly fool your body clock into thinking it’s morning. Sunshine is ideal, but those sun-mimicking “happy” lights designed to counter seasonal affective disorder are a good stand-in, Jain says. (See sidebar for details.)

A walk might help, too, Jain says. Though its effects are much weaker than light’s, exercise (especially when vigorous) has a similar influence and can make you feel more alert.

If these tricks sound too complicated or haven’t worked for you in the past, there are both natural and prescription aids.

Melatonin, a hormone normally excreted during sleeping hours, can help shift your circadian clock by inducing drowsiness. Though Jain cautions that the studies on melatonin are mixed, a review of 10 studies by the Cochrane Collaboration, an independent research group, concluded that melatonin can be “remarkably effective” at reducing jet lag, and the American Academy of Sleep Medicine guidelines suggest that a dose of 0.5 to 5 milligrams of melatonin taken at bedtime may help you adjust when traveling east.

Your doctor may be willing to prescribe a short-acting sleeping pill. It won’t reset your body clock, Jain says, but it may help you get the rest you need to work or enjoy your vacation despite jet lag. Such drugs can cause serious side effects, however, including amnesia and confusion, so if your doctor does give you a prescription, try it out at home first before you use it during travel, Jain says.

I’ve never tried melatonin or pills, but on my last business trip to Geneva, I tested the light strategy when I got to my destination. I’d arrived in the dead of winter, so I used a “happy light” during the morning hours and went running outdoors when the sun came out. I can’t say it completely eliminated my grogginess, but it got me through my workdays and even allowed me to stay awake past dinnertime.